In constructing concrete masonry walls, concrete masonry units are generally stacked so that vertical cores are aligned to form an unobstructed, continuous series of vertical spaces within the wall. Head joints (i.e., vertical spaces between adjacent masonry units) and bed joints (i.e., horizontal spaces between adjacent masonry units) must be grouted to properly bond the units together. If the wall is partially grouted, the cross webs adjacent to the cores to be grouted are mortared to confine the grout flow. If the wall is solidly grouted, the cross webs need not be mortared since the grout flows laterally, filling all spaces.
In certain instances, full head joint mortaring should be considered when solid grouting since it is unlikely that grout will fill the space between head joints that are only mortared the width of the face shell (e.g., when penetration resistance is a concern such as tornado shelters and prison walls). In such cases, open end or open core units should be considered as there is no space between end webs with these types of units. Care should be taken to prevent excess mortar from extruding into the grout space. Mortar that projects more than ½ inches into the grout space must be removed. This is because large protrusions can restrict the flow of grout, which will tend to bridge at these locations, potentially causing incomplete filling of the grout space. To prevent bridging, grout slump is generally required to be between eight and eleven inches at the time of placement. This slump may be adjusted under certain conditions such as hot or cold weather installation, low absorption units or other project specific conditions. Approval should be obtained before adjusting the slump outside the requirements. Using the grout demonstration panel option in Specification for Masonry Structures is an excellent way to demonstrate the acceptability of an alternate grout slump.
At the footing (e.g., base portion of a wall), mortar bedding under the first course of block to be grouted should permit grout to come into direct contact with the foundation or bearing surface. If foundation/footer dowels are present, they should align with the cores of the masonry units. If a dowel interferes with the placement of the units, it may be bent a maximum of one inch horizontally for every six inches vertically. When walls will be solidly grouted, saw cutting or chipping away a portion of the web to better accommodate the dowel may also be acceptable. If there is a substantial dowel alignment problem, the project engineer must be notified.
In prior art systems, vertical reinforcing steel is typically placed into position before the masonry units are stacked. When vertical reinforcements are placed prior to laying block, the use of open-end “A” or “H” shaped units will allow the units to be placed around the reinforcing steel. It is required that both horizontal and vertical reinforcement be located within tolerances and secured to prevent displacement during grouting. Laps are made at the end of grout pours and any time the bar has to be spliced. Reinforcement can be spliced by either contact or noncontact splices. Noncontact lap splices may be spaced as far apart as one-fifth the required length of the lap but not more than eight inches per Building Code Requirements for Masonry Structures. This provision accommodates construction interference during installation as well as misplaced dowels. Splices are not required to be tied, however tying is often used as a means to hold bars in place.
As the wall is constructed, horizontal reinforcement can be placed in bond beam or lintel units. If the wall will not be solidly grouted, the grout may be confined within the desired grout area either by using solid bottom masonry bond beam units or by placing plastic or metal screening, expanded metal lath or other approved material in the horizontal bed joint before laying the mortar and units being used to construct the bond beam.
Using “A” or “H” block units to construct a wall with prior installed vertical reinforcements has several disadvantages. In particular, extra care must be taken to prevent excess mortar from extruding into the grout space due to the open ends of the “A” or “H” block units, “A” and “H” block units have a higher break rate due to their open ends, and laying “A” or “H” units after a reinforcement system has been put in place requires additional time in arranging the units correctly.
What is needed therefore is an efficient and effective system for providing vertical reinforcing bars after concrete masonry units have been positioned for constructing a concrete masonry wall. An efficient and effective system for coupling reinforcing bars together is also desired regardless of whether the bars are positioned pre-wall erection or post-wall erection.